JAKARTA, Indonesia (AP) — Rebels in Indonesia’s Papua province demanded that the government hold negotiations on their territory’s self-determination and warned of more attacks following a raid on a construction site that left at least 16 dead.

An insurgency has simmered in Papua since the early 1960s, when Indonesia annexed the region that was a former Dutch colony. It was formally incorporated into Indonesia in 1969 after a U.N.-sponsored ballot that was seen as a sham by many.

Sebby Sambom, spokesman for the West Papua National Liberation Army, the military wing of the Free Papua Movement, said in a telephone interview Friday that they attacked a government construction site last weekend because they believe the project is conducted by the military.

Security forces have retrieved the bodies of 16 workers hired to build bridges on a section of the trans-Papua road, Papua police spokesman Suryadi Diaz said.

Authorities believe the armed group killed 19 workers, based on the accounts of survivors. They have rescued 24, including seven workers, and are searching for two missing as well as the bodies of three others. A soldier at a military post near the site was also killed.

Indonesian President Joko “Jokowi” Widodo has ordered the military and police to arrest the perpetrators of the worst separatist attack during his administration and said he will not tolerate “armed criminals” in Papua or the rest of the country.

He said the attack will not dissuade his government from continuing to develop Papua, including the 4,600-kilometer (2,875-mile) trans-Papua road, which his administration has claimed is widely supported by local people.

The road, which will stretch from Sorong in West Papua province to Merauke in Papua province, is expected to be completed next year and help boost economic development in both provinces.

“Trans-Papua road projects are being carried out by Indonesian military and that is a risk they must bear,” Sambom said. “We want them to know that we don’t need development, what we want is independence.”

Indonesia’s government, which for decades had a policy of sending Javanese and other Indonesians to settle in Papua to dilute the number of indigenous people, is now trying to spur economic development to dampen the separatist movement.

“Our leaders have declared a war zone since last year and warned that the trans-Papua road construction should be stopped, but Indonesia has ignored it,” Sambom said.

He called for the government to agree to peace talks similar to ones that led to another province, Aceh, becoming semiautonomous, or a “real referendum” on independence as occurred in the former Indonesian territory of East Timor.

“If Aceh and East Timor can get that opportunity, why don’t we?” said Sambom, who said he was speaking from an area near the border with neighboring Papua New Guinea.

National police chief Tito Karnavian estimated the strength of the armed group at not more than 50 people with about 20 weapons, and said more than 150 police and soldiers had been sent to restore security in Nduga district, a stronghold of the separatists.

Sambom, however, claimed the rebels have 29 operational area commands in Papua, each with 2,500 members.